1. Field of the Invention
This invention relates to a respiratory mask, more particularly to a respiratory mask including an adjustment unit.
2. Description of the Related Art
Referring to FIG. 1, a conventional respiratory mask 11 includes a mask body 111 adapted to cover a user's nose and/or mouth, and a forehead support unit 112 mounted on the mask body 111 for supporting the user's forehead. An air supply tube 13 is connected to the mask body 111 for providing a passage of a positive pressure airflow into the respiratory mask 11.
In use, head straps 14 are respectively inserted through two opposite sides of the forehead support unit 112 and the mask body 111, and extend around a rear side of the user's head. Subsequently, the head straps 14 are tightened so as to respectively secure the forehead support unit 112 and the mask body 111 to the user's forehead and cheeks, such that a central portion of the mask body 111 covers the user's nose and/or mouth to provide an abutment pressure against the root of the nose.
However, strength of the abutment pressure against the root of the nose varies with facial differences, such as forehead shape, cheek shape, and nose shape. For example, when the user has a concave or flat nose shape, there is a weak abutment pressure against the root of the nose that a gas tight seal of the respiratory mask 11 is not achieved, which results in leakage of the airflow. Conversely, the user with a convex or straight nose shape may feel a strong applied abutment pressure and becomes uncomfortable when wearing the respiratory mask 11 for a long period of time. Therefore, the respiratory mask 11 having an invariable size is not suited for accommodating a variety of facial differences among individuals.
U.S. Pat. No. 6,532,961 discloses an adjustable respiratory mask having a structure similar to that of the conventional respiratory mask 11. The adjustable respiratory mask includes a forehead support unit that has a cushion frame abutting against a user's forehead, and a joining member adjustably mounted between a mask body and the forehead support. The joining member is adjustable to change an angle between the cushion frame and the mask body to suit the wearer's forehead topography.
However, such angular adjustment does not alter the abutment pressure against the root of the user's nose.